The present disclosure relates to fluid fittings, and more particularly, to an improved fitting employing complementary fitting materials which allow the fitting to maintain a tight leak seal during and post exposure to extreme heat. In one embodiment, a fitting includes a connector body having a sleeve that receives a tube or pipe therein and includes at least one radially extending seal for sealing and mechanically connecting to the tube or pipe when a swage ring is axially installed on the sleeve. The improved fitting will be described with particular reference to this embodiment, but it is to be appreciated that the improved fitting may relate to other similar environments and applications.
Various types of fittings have been developed for joining tubes and pipes to other tubes and pipes, or to other fluid apparatus such as pumps, fluid motors, actuation cylinders, supply tanks and canisters, etc. For thin walled tubing or pipe, various types of fittings are used which compress against the outside diameter of the tube or pipe to create a seal. One particular type of such a fitting includes a coupling body and a swage ring which is forced over the coupling body to compress it radially inwardly against a tube or pipe received within the coupling body to create a mechanical connection and seal. Generally, this type of fitting has one or more circumferential teeth or ridges on an inside diameter of the coupling body which, when compressed inwardly by a swage ring, engage the outside diameter of the tube or pipe to create one or more leak-tight mechanical connections or joints between the tube or pipe and the fitting. This engagement of the sealing teeth of the fitting with the tube or pipe causes the pipe to be deformed radially inwardly, with the coupling body of the fitting located externally about the tube or pipe.
Examples of such mechanically attached fittings are provided in U.S. Pat. Nos. 4,482,174; 5,110,163; 5,114,191; 6,692,040; and U.S. patent application Ser. No. 11/065,656. One example of an installation tool employable for attaching these types of fittings to a tube or pipe is described in U.S. Pat. No. 5,305,510. All the teachings and substance of these patents are hereby expressly incorporated by reference into the present application.
The assignee of this application, Lokring Technology Corporation, manufactures, sells and/or distributes a variety of such fittings. These fittings often include three (3) circumferential teeth or ridges, typically referred to as seals, including a main seal, an inboard seal and an outboard seal. The particular configuration of the fitting body and/or the swage ring often determines the order in which the seals (including the main, inboard and outboard seals) are forced into deforming contact with the tube or pipe. Some three-seal fittings of Lokring are configured for applying a kick down force to the main seal. Thus, after a particular surface of the swage ring forces the main seal into deforming contact with the tube or pipe, a second, diametrically smaller surface of the swage ring further forces the main seal into the tube or pipe. Like the order in which the inboard and outboard seals deformingly contact the tube or pipe, the sequential order in which the kick down force is applied to the main seal varies from fitting to fitting.
Typically, the fitting body and the swage ring are formed of any of a variety of fitting materials, including, for example, stainless steel, carbon steel, 90/10 copper nickel alloy (90% copper, 10% nickel), and 70/30 copper nickel alloy (70% copper, 30% nickel). These types of mechanical fittings are prevalent in the art, and have proven effective in connecting tubes and pipes formed of any of a variety of materials to one another to provide a fluid or vapor connection. Copper-nickel fittings used in conjunction with a tube or pipe formed of 70/30 copper nickel are often used in environments, such as marine environments, where high corrosion resistance is required and where concern over chloride stress-corrosion cracking prevents use of stainless steel.
Nevertheless, even such 70/30 copper nickel swage mechanical fittings can be inadequate and occasionally prone to failure when employed in these types of environments under certain conditions, such as after exposure to extreme heat which approaches the annealing temperature of 70/30 copper nickel (e.g., between approximately 1200° F. (648° C.) and approximately 1500° F. (815° C.)). As is well-known, annealing is a process involving heating and cooling designed to effect relief of, among other things, residual stress. The construction of the above described swaged mechanical fittings are such that the seal between the fitting and the tube or pipe is maintained by the tensile preload placed on the swage ring and the compressive preload placed on the tube or pipe. If the fitting and tube or pipe is exposed to temperatures which approach or reach the annealing temperature, the preload stresses may have a tendency to relax and develop a gap between the seals and the tube or pipe and leak.
One method proposed to overcome the potential metallurgical shortcomings of the 70/30 copper nickel fitting is to use a swage ring made of a material that does not anneal at the annealing temperature of 70/30 copper nickel. This differing material arrangement is possible because the swage ring does not come into contact with the fluid being conveyed. One such material that can be used for the swage ring is 316 stainless steel. However, and as indicated above, stainless steel is prone to corrode in salt water. Thus, for this type of fitting to work as intended, over extended periods of time, the fitting must be placed in an exterior environment devoid of salt water or salt laden air, a difficult task in the marine environment typically encountered where 70/30 copper nickel tube or pipe is often used.
Accordingly, the present invention provides an improved swage mechanical fitting having complementary materials which overcomes difficulties associated with the prior art while providing better and more advantageous overall results.